A rig owned by Diamond Offshore will leave the Gulf of Mexico to work for BP Plc in Vietnam, marking another exit after BP's spill last year led to a moratorium on deepwater drilling.

The Ocean Monarch, a deepwater rig now working for Marathon Oil Corp on a daily rate of about $290,000, will earn $340,000 per day on a three-month contract in Vietnam with the British oil company starting in November, according to Diamond Offshore Drilling Inc's fleet status report on Tuesday.

Seven of the more than 30 rigs working in the US Gulf in April 2010 have departed, although one has returned and two more could come back later this year.

Also, Exxon Mobil Corp is expected to move a newly built Transocean Ltd deepwater rig to the Gulf late next year after working in the Black Sea.

The rig is the third owned by Diamond to leave the Gulf. Diamond also said in its fleet report that the first rig to depart, the Ocean Endeavor, signed an eight-month extension of the one-year contract it had with Egypt's Burullus Gas Co. Once the Monarch leaves, the Houston-based company will have just one deepwater rig left in the nearby waters.

The US deepwater drilling moratorium followed BP's well blow-out in April 2010, which killed 11 people and destroyed a Transocean rig. However, regulators resumed issuing permits in the past four months, including for eight new wells.

Marvin Odum, president of Shell Oil Co, told the Reuters Global Energy and Climate Summit on Monday that it was good to see the process moving again, but added: "We really need to see that machine pick up speed again."